1. Field of the Invention
The invention relates to a power semiconductor circuit comprising a gate-turn-off semiconductor component and a diode.
2. Discussion of Background
In order to be driven, the new, fast, gate-turn-off power semiconductor components, which are increasingly being applied in power electronics, such as, for example, the FCTh (Field Controlled Thyristor), the IGBT (Insulated Gate Bipolar Transistor), the MCT (MOS Controlled Thyristor) or the HF-GTO, require short current pulses having very high rates of current rise di/dt.
In order to be able to achieve such high di/dt values, total values of only a few nH or, possibly, of &lt;1 nH are permissible for the inductance L of the drive circuit. An arrangement of the drive circuit outside the component case, and feeding the control pulses by coaxial cable, for example, are therefore no longer possible.
A solution to this problem emerges from the U.S. Pat. No. 5,027,192. It is a matter here of a fast power semiconductor circuit of the type mentioned at the beginning. The essential part of this older application concerns a flexible stripline as a low-inductance connection between the semiconductor component and drive circuit.
The recently developed latching, fine-structure, bipolar semiconductor components such as, for example, FCTh, FSGTO (Fine-Structure GTO) or SITh, exhibit greatly improved turn-off characteristics when driven very fast (rise time of the gate current &lt;200 ns). They then permit fast processing of high currents and voltages (dV.sub.a /dt&gt;10 kV/.mu.s, I.gtoreq.100 A, U&gt;2 kV). In this case, bulky and complicated snubber circuits, such as are presently unavoidable with GTOs, can be completely eliminated, as a rule. It is, however, a precondition that the reverse recovery of the free wheeling diodes cannot cause any excessive voltage peaks on parasitic inductances.
In the IGBTs restricted to low voltages (&lt;1 kV), reverse recovery of the free wheeling diodes and commutation voltage peaks lead to problems if sizeable currents (&gt;100 A) are to be switched. In order to avoid these, it is therefore necessary to use either snubbers, once again, or resistors in the input circuit to slow down the drive rate (see, for example, "Switching Performance of a new fast IGBT", L. Lorenz, G. Schulze, PCI--June 1988 Proceedings, pages 189-202). Similarly, fast fine-structure bipolar transistors (for example SIRET =SIEMENS Ring Emitter Transistor) also suffer from overvoltage peaks in the turn-off process. In practice, therefore, they are in no way capable of being applied with the full switching rate.